The ever-changing demands of global commerce, coupled with the almost unlimited capabilities of state-of-the-art imaging systems, has resulted in a need for a wide variety of document types and formats. The days of "letter or legal" have gone the way of carbon paper and mimeographs. Imaging systems are capable of handling a variety of standard sizes, such as letter, legal, A4, and A5-ISO, as well as custom sheet sizes.
Rather than require system users to have on hand a different sheet tray for each sheet size, it is known to provide cassette trays having the ability to handle a relatively wide range of sizes. Such trays typically are provided with sliding rear adjusts to accommodate different sheet lengths, and/or sliding side adjusts to accommodate different sheet widths. A spring-biased lift plate is typically provided to urge the sheet stack towards an infeed mechanism, such as feed rollers and the like.
It has been found that the difference in weight between smaller and larger sheet sizes can present problems. For example, if the spring bias of the lift plate is chosen for an "average" sheet size, heavier sheet stacks can have "no-pick" problems, where the spring bias is insufficient to overcome the weight of the stacks while still providing the necessary pick force. At the other end of the spectrum, smaller sheets may have "multi-feed" problems, wherein the pick force exceeds the separation force so that two or more sheets are fed into the feed mechanism simultaneously.
One proposed solution to these problems is to provide manual spring adjustments, where system users are required to adjust various levers and knobs corresponding to individual sheet sizes.
Unfortunately, this solution presents problems of its own. For instance it is difficult or impossible for users to adjust for non-standard sizes. Further, the requirement for independent manual adjustment by the user is inconvenient, and may be easily overlooked.
It is therefore apparent that the need exists for a sheet material tray having a simple, reliable mechanism that will automatically adjust spring bias to paper size without any additional mechanical manipulation by the system user.